The primary focus of work with eukaryotic vectors has shifted during the past year to investigation of growth inhibitory activity detected in a DNA-mediated gene transfer system. Progress has been made in defining the range of cell types from which genomic DNA demonstrating strong growth inhibitory activity can be prepared. Molecular cloning of growth inhibitory sequences is being pursued by analysis of a cosmid library derived from WI38 human embryo fibroblast genomic DNA. Both serial gene transfer and fractionation ("sib selection") techniques have been employed, with the result that a single candidate cosmid clone exhibiting high growth inhibitory function was identified. Studies on growth-stimulatory genes concentrated on characterization of c-H-ras transformed rat embryo fibroblasts with respect to tumorigenicity and metastatic phenotype. Continuing efforts to improve gene transfer technology involved developmental experiments on vectors that code for novel cell surface antigens, further application of a vector system based on the bacteriophage lambda lysogenic cycle, and preparation of helper virus-free retrovirus/dihydrofolate reductase vector stocks for infection of mouse bone marrow cells.